滇西北金沙江结合带霞若—拖顶地区两类中-基性火山岩的多元地球化学示踪

MULTIPLE GEOCHEMICAL TRACES OF TWO TYPES OF INTERMEDIATE-BASIC VOLCANIC ROCKS IN XIARUO-TUODING AREAS, JINSHA RIVER COMBINATION ZONE, NORTHWEST OF YUNNAN PROVINCE, CHINA

应用常量元素、微量元素对火山岩进行构造环境、成因及岩源示踪时 ,首先必须在宏观区域地质、地球化学调查基础上 ,结合当时所形成的各类地质体岩石类型组合来恢复 ,它是宏观构造环境判别的基础 ;其次 ,由于构造环境时空复杂性 ,需采用“两结合”的研究方法 ,一是多元地球化学信息示踪 ,二是不同岩类的时空配套 ;第三 ,在选择判别图解时 ,弄清前人图解的应用前提、适用范围和条件 ,切忌乱套瞎投 .在此思想指导下 ,侧重对滇西北金沙江结合带霞若—拖顶地区两类中 -基性火山岩进行了多元地球化学示踪 ,获得了较好的效果 :(1)金沙江蛇绿混杂岩带东侧的基性火山岩产于大陆裂谷环境 ,而西侧中 -基性火山岩具岛弧火山岩特征 ;(2 )两者火山熔浆均源自富集地幔 ,东侧来自均一的富集地幔 ,而西侧富集地幔具不均一性 ;(3)在此基础上讨论了它们形成的构造演化特征 .

When using major and trace elements as a tool to trace tectonic settings,origins and magma sources of volcanic rocks,we must firstly reconstruct the elements on the bases of macro-regional geology and geochemical investigations,and of various kinds of rock-type assemblages in different geological bodies that occurred at that time. This reconstruction serves as the basis for the identification of the macro-tectonic settings. Secondly,we should adopt the research method characterized by the combination of the multiple geochemical information tracing with the temporal-spatial matching of various kinds of rock types, due to the temporal-spatial complexity of the tectonic settings. Thirdly,we should fully understand the application premises,ranges and conditions, so as to identify correctly the corresponding illustrations. On the basis of the three points mentioned above, this paper focuses on the multiple geochemical tracing of the two types of intermediate-basic volcanic rocks in Xiaruo-Tuoding areas in the Jinsha River combination zone, Northwest of Yunnan Province, China. This research has already brought us the following three relatively excellent effects: (1) The basic volcanic rocks located on the eastern side of the Jingsha River ophiolitic mélange zone occurred in the continental-rift setting. However, the intermediate-basic volcanic rocks are characterized by the island-arc volcanic rocks on the western side of Jingsha River ophiolitic mélange zone. (2) The volcanic lava of the two types of volcanic rocks both originated from the lava-enriched earth mantle. Specifically, the volcanic rock on the eastern side originated from the homogeneous lava-enriched earth mantle, while those on the eastern side originated from the heterogeneous lava-enriched earth mantle. (3) Finally, the structural evolutionary characteristics of these volcanic rocks are discussed.